JP5131920B2 - Carbon dioxide immobilization apparatus and method - Google Patents

Description

  The present invention relates to a carbon dioxide immobilization apparatus and method for immobilizing carbon dioxide by reducing carbon dioxide by a photocatalytic reaction to produce carbon dioxide reduction products such as formic acid, formaldehyde, and methanol.

  Carbon dioxide is known as a greenhouse gas that is the main cause of global warming, and its immobilization method and effective utilization method are being studied. For example, in Patent Document 1, a photocatalyst is dispersed in an aqueous solution containing carbon dioxide, and carbon dioxide is reduced by irradiating the aqueous solution with ultraviolet light to produce formic acid, formaldehyde, methanol, methane, etc. A method for immobilization is disclosed.

The reduction reaction of carbon dioxide in Patent Document 1 is a reaction similar to the photosynthetic action of plants, and is a reaction that is attracting attention as an energy generation method by artificial photosynthesis, but its reaction efficiency is poor and the yield is extremely low. In order to improve the reaction efficiency, Patent Document 2 and Patent Document 3 propose a composite photocatalyst composed of a semiconductor photocatalyst component and a carbon dioxide reduction catalyst component.
JP-A-55-105625 JP 2003-275599 A JP 2004-59507 A

  In the carbon dioxide reduction method using the composite photocatalysts of Patent Document 2 and Patent Document 3, the reduction of carbon dioxide is performed using sunlight, but the reaction using sunlight takes time and Since a condensing device (Patent Document 2, FIG. 2) for efficiently condensing and irradiating the reactor with light is required, it is difficult to increase the size of the reactor.

  In Patent Document 2 and Patent Document 3, artificial light may be used instead of sunlight, but the reaction using the composite photocatalyst requires a reaction temperature of about 300 ° C. to generate methanol. (Patent Document 3), an energy cost for raising the reactor to around 300 ° C. is required.

  An object of the present invention is to fix carbon dioxide by performing a reduction reaction of carbon dioxide by a photocatalyst with high efficiency and low cost (low energy) and generating a carbon dioxide reduction product by the reduction reaction to fix the carbon dioxide. An object of the present invention is to provide a gasification device and a method for immobilizing carbon dioxide.

  In order to solve the above problems, a carbon dioxide immobilization apparatus according to a first aspect of the present invention includes a microreactor having a microchannel through which a gas source and a liquid source are circulated as a reaction source, and the microstream A gas raw material feeding means for feeding a gas raw material into the path; a liquid raw material feeding means for feeding the liquid raw material into the microchannel; and a photocatalyst layer provided on the inner surface of the microchannel, wherein the gas raw material is carbon dioxide. The liquid material is a material capable of reacting with carbon dioxide to produce an organic compound, the gas material feeding means and the liquid material feeding means, the liquid material flows along the inner surface of the microchannel, It is configured to be capable of forming a pipe flow in a state where carbon dioxide flows through the central portion.

  The carbon dioxide immobilization apparatus of this embodiment is a device that performs a reaction with a photocatalyst using a liquid raw material as a medium on carbon dioxide, which is a gas raw material, to fix the carbon dioxide. The reaction by the photocatalyst is a reaction for reducing carbon dioxide, and a carbon dioxide reduction product is generated from carbon dioxide. That is, carbon dioxide, which is a gaseous raw material, is immobilized as a carbon dioxide reduction product.

  According to the present invention, among the reaction raw materials, carbon dioxide, which is a gaseous raw material, is used to form a pipe flow (a state where the liquid raw material flows along the inner surface of the microchannel and the carbon dioxide flows through the central portion). The liquid raw material in which carbon dioxide is dissolved in a saturated state can be forcibly localized near the surface of the photocatalyst layer and passed through the microchannel in a laminar flow state to perform the photocatalytic reaction. In this way, the liquid raw material flowing along the inner surface of the micro flow path is hereinafter referred to as “cylindrical liquid film flow”, and the carbon dioxide flowing through the center of the pipe flow is hereinafter referred to as “central gas flow”. There is.

Furthermore, since carbon dioxide, which is a gaseous raw material, also comes into contact with the liquid raw material in the vicinity of the photocatalytic layer, even if carbon dioxide dissolved in the liquid raw material is consumed as the photocatalytic reaction proceeds, carbon dioxide is immediately extracted from the central gas stream. Is dissolved (supplemented) in the liquid raw material, and the carbon dioxide in the liquid raw material maintains its saturated concentration state even when the photocatalytic reaction proceeds. Therefore, the concentration of carbon dioxide dissolved in the liquid raw material can be always kept constant in a saturated state in the vicinity of the photocatalyst layer over the entire length of the microchannel, and the equilibrium of the photocatalytic reaction can be maintained. The reduction reaction proceeds mainly, and the production amount of the carbon dioxide reduction product can be kept increasing. Eventually, the photocatalytic reaction reaches an equilibrium state by increasing the amount of carbon dioxide reduction product corresponding to the saturation concentration of carbon dioxide.
Thus, the amount of carbon dioxide reduction products generated by the photocatalytic reaction can be effectively increased by having the carbon dioxide at a saturated concentration in the entire length of the microchannel and in the vicinity of the photocatalyst layer.

  In this way, a liquid raw material that can react with carbon dioxide to produce an organic compound is used as a reaction medium, and the photoreduction reaction of carbon dioxide is performed. Therefore, carbon dioxide is efficiently produced using the organic compound as a carbon dioxide reduction product. Can be immobilized. For example, when water is used as a liquid raw material that can react with carbon dioxide to produce an organic compound, carbon dioxide can be immobilized using formic acid, formaldehyde, methanol, or methane as a carbon dioxide reduction product.

The carbon dioxide immobilization reaction by the carbon dioxide immobilization apparatus of this embodiment will be described with a specific example. Hereinafter, a case where water (H ₂ O) is used as a liquid raw material that can react with carbon dioxide to produce an organic compound will be described.

  The photoreduction reaction of carbon dioxide is generally explained by a multi-electron reduction reaction as shown in the following formulas (1) to (5).

Although details of these reaction mechanisms are not clarified, a reduction mechanism as shown in the formulas (1) to (5) can be considered directly on the solid surface of the photocatalyst.

  Here, since the photocatalytic reaction is a reaction involving a reverse reaction, if the organic compound produced by the reaction with carbon dioxide is present in the reaction system (in the cylindrical liquid film flow of the liquid raw material), the reverse reaction of the reduction reaction ( Oxidation reaction) causes the produced organic compound to return to carbon dioxide. However, when a pipe flow consisting of a cylindrical liquid film flow and a central gas flow is formed, among the organic compounds produced by reacting with carbon dioxide in the liquid raw material, the vapor pressure is high, or Organic compounds with low solubility (hereinafter sometimes referred to as high vapor pressure or low solubility organic compounds) move from the cylindrical liquid film flow into the central gas flow (see FIG. 1).

Then, the high vapor pressure or low solubility organic compound moves into the central gas flow, and carbon dioxide, which is a gaseous raw material, moves into the cylindrical liquid film flow, and the cylindrical liquid film flow (liquid raw material) As shown in the graph of FIG. 1, the carbon dioxide concentration therein is maintained at a constant saturation concentration over the entire length of the channel length of the microchannel.
On the other hand, when a liquid material saturated with carbon dioxide is circulated through the microreactor (without pipe flow) without forming a pipe flow, the carbon dioxide concentration in the liquid material passes through the microchannel. It decreases as the reaction proceeds.

  An organic compound having a low vapor pressure or an organic compound having a high solubility in a liquid raw material tends to remain in the cylindrical liquid film flow, and can be obtained as it is as a product of the organic compound or by a subsequent photocatalytic reaction. In some cases, the organic compound is generated or disappears by a reverse reaction.

  In addition, the vapor pressure is “high” or the vapor pressure is “low” means that the vapor pressure is relatively high, and an organic compound having a high vapor pressure is higher than an organic compound having a low vapor pressure. The explanation is based on the tendency to become gas, and the specific value of the vapor pressure is not limited.

FIG. 2 is a diagram showing a reaction when water (H ₂ O) is used as a liquid raw material. Organic compounds generated when water (H ₂ O) is used as the liquid raw material are formic acid, formaldehyde, methanol, and methane. Methane (CH ₄ ) has a high vapor pressure and low solubility in water, which is a liquid raw material, and therefore easily moves into the central gas stream. In this way, the generated organic compound escapes from the reaction system (in the cylindrical liquid film flow of the liquid raw material), so that the reverse reaction by the photocatalyst of the once generated organic compound is prevented, so that the vapor pressure is high, or An organic compound having low solubility in the liquid raw material can be obtained efficiently.

  In addition, the photocatalyst has different affinity for the solvent depending on the type. For example, the aforementioned titanium dioxide has a high affinity with an aqueous solvent, but has a low affinity with a hydrophobic organic solvent. In the case of a batch system in which titanium dioxide having such properties is dispersed in a liquid raw material, an organic solvent having a low affinity for the photocatalyst cannot be used as the liquid raw material.

  According to the present invention, even when the liquid raw material has a low affinity for the photocatalyst, the total amount thereof is localized near the surface of the photocatalyst layer by forming the pipe flow with carbon dioxide. It is possible to pass through the microchannel, and carbon dioxide can be immobilized using a solvent having a low affinity for the photocatalyst as a reaction medium.

  The carbon dioxide immobilization apparatus according to the second aspect of the present invention is characterized in that, in the first aspect, the photocatalyst is titanium dioxide.

  According to this invention, it can be set as the fixing device of the carbon dioxide which has the high photocatalytic activity of titanium dioxide. Titanium dioxide is a photocatalyst that is highly transparent when provided as a photocatalyst layer and has excellent durability, and is excellent in that it has stable photocatalytic activity. In addition, it is easy to form a titanium dioxide layer, and since the raw material is inexpensive, a photocatalytic layer can be provided at low cost.

  In the carbon dioxide immobilization apparatus according to the third aspect of the present invention, in the second aspect, any one metal of ruthenium, rhodium, palladium, platinum, copper, silver, and gold is added to the titanium dioxide. It is characterized by being supported as a cocatalyst.

  According to the present invention, the photocatalytic activity of titanium dioxide can be further enhanced by the promoter action of any one metal of ruthenium, rhodium, palladium, platinum, copper, silver, and gold supported on titanium dioxide. .

  In the method for immobilizing carbon dioxide according to the fourth aspect of the present invention, carbon dioxide is used as a gas source in the microchannel of a microreactor having a photocatalyst layer on the inner surface of the microchannel, and the carbon dioxide is used as a liquid source. A photocatalyst is formed by feeding a raw material capable of reacting with an organic compound to form an organic compound, forming a pipe flow in a state where the liquid raw material flows along the inner surface of the micro flow channel and carbon dioxide flows through the central portion in the micro flow channel The organic compound is produced from carbon dioxide by advancing the reaction to fix the carbon dioxide.

  According to the present invention, among the reaction raw materials, carbon dioxide, which is a gaseous raw material, is used to form a pipe flow, and the liquid raw material in which carbon dioxide is dissolved in a saturated state is forcibly localized near the surface of the photocatalyst layer. The photocatalytic reaction is performed by passing through the microchannel in a laminar flow state. That is, the carbon dioxide that has migrated from the carbon dioxide flowing in the center of the pipe flow into the liquid raw material that flows along the inner surface of the micro-flow path is caused to proceed by a reduction reaction by the photocatalyst and is generated by the reduction reaction. Carbon dioxide can be immobilized as a carbon dioxide reduction product.

Since carbon dioxide, which is a gaseous raw material, also comes into contact with the liquid raw material in the vicinity of the photocatalyst layer, even if the carbon dioxide dissolved in the liquid raw material is consumed as the photocatalytic reaction proceeds, the carbon dioxide immediately becomes liquid from the central gas stream. The carbon dioxide in the liquid raw material is dissolved (supplemented) in the raw material, and the saturated concentration state is maintained even if the photocatalytic reaction proceeds. Therefore, the concentration of carbon dioxide dissolved in the liquid raw material can be always kept constant in a saturated state in the vicinity of the photocatalyst layer over the entire length of the microchannel, and the equilibrium of the photocatalytic reaction can be maintained. The reduction reaction proceeds mainly, and the production amount of the carbon dioxide reduction product can be kept increasing. Eventually, the photocatalytic reaction reaches an equilibrium state by increasing the amount of carbon dioxide reduction product corresponding to the saturation concentration of carbon dioxide.
Thus, the amount of carbon dioxide reduction products generated by the photocatalytic reaction can be effectively increased by having the carbon dioxide at a saturated concentration in the entire length of the microchannel and in the vicinity of the photocatalyst layer. That is, the photocatalytic reaction can proceed with high efficiency.

  Further, among the organic compounds produced by reacting with carbon dioxide in the cylindrical liquid film flow of the liquid raw material, the organic compound having a high vapor pressure moves into the central gas flow of the pipe flow. The organic compound produced by the reaction with carbon dioxide escapes from the reaction system (in the cylindrical liquid film flow of the liquid raw material) into the central gas flow, so that the reverse reaction (oxidation reaction) of the organic compound once produced by the photocatalyst Is prevented, and an organic compound having a high vapor pressure can be obtained efficiently.

In the method for immobilizing carbon dioxide according to a fifth aspect of the present invention, in the fourth aspect, the liquid raw material is water, and at least one compound of formic acid, formaldehyde, and methane is used as a carbon dioxide reduction product. It is made to generate.
According to the present invention, carbon dioxide can be fixed as formic acid, formaldehyde, or methane.

  The carbon dioxide immobilization method according to a sixth aspect of the present invention is characterized in that, in the fourth aspect, the liquid raw material is water, and methanol is generated as a carbon dioxide reduction product.

  According to the present invention, among the reaction raw materials, the carbon raw material, which is a gaseous raw material, is used to form a pipe flow, and the liquid raw material capable of generating an organic compound is forcibly localized near the surface of the photocatalyst layer. Thus, the microchannel can be passed in a laminar flow state. Furthermore, since carbon dioxide, which is a gaseous raw material, also comes into contact with the liquid raw material in the vicinity of the photocatalytic layer, even if carbon dioxide dissolved in the liquid raw material is consumed as the photocatalytic reaction proceeds, carbon dioxide is immediately extracted from the central gas stream. Is dissolved (supplemented) in the liquid raw material, and the carbon dioxide in the liquid raw material maintains its saturated concentration state even when the photocatalytic reaction proceeds. Thereby, the production amount of the carbon dioxide reduction product by the photocatalytic reaction can be effectively increased. That is, the effect that the photocatalytic reaction can be advanced with high efficiency is obtained.

  By using the liquid raw material which can produce | generate the said organic compound as a reaction medium by this, the reaction which produces | generates an organic compound from a carbon dioxide is performed with high efficiency, and various reduction | restoration reactions are performed by performing further photoreduction reaction from the produced | generated organic compound. Carbon dioxide can be immobilized as a carbon dioxide reduction product.

Example 1
An example of an embodiment of the present invention will be described with reference to FIGS.
FIG. 3 is a perspective view showing the carbon dioxide immobilization apparatus according to the present embodiment. 4 is a cross-sectional view taken along the line II of FIG. FIG. 5 is an enlarged view of a portion A of the II-II cross section of FIG. 4 and shows a pipe flow state in the micro flow path. 6 is a sectional view taken along line III-III in FIG.

  The carbon dioxide immobilization apparatus 1 according to the present embodiment includes a microreactor 10 that is made of a light transmissive material and has a microchannel 4 through which a gas raw material and a liquid raw material are circulated as a reaction raw material. The microreactor 10 having the microchannel 4 is, for example, a substrate formed of a light-transmitting material such as borosilicate glass, quartz, and acrylic resin provided with a groove 6 (FIG. 6) forming the microchannel 4. 2 and the top plate 3 can be joined together.

Grooves 6 are formed on the surface of the substrate 2 by etching or machining. The groove 6 is provided with a photocatalyst layer 5 as shown in FIG. In this embodiment, titanium dioxide (TiO ₂ ) is used as the photocatalyst. Of course, the photocatalyst is not limited to titanium dioxide. Furthermore, the titanium dioxide photocatalytic activity can be further enhanced by supporting a metal acting as a promoter such as ruthenium, rhodium, palladium, platinum, copper, silver, gold, etc. If a visible light responsive photocatalyst is used, it is possible to use sunlight as an excitation light source for the photocatalyst.

  The microchannel 4 is formed by joining the substrate 2 provided with the groove 6 provided with the photocatalyst layer 5 and the top plate 3. The cross-sectional shape of the microchannel 4 is not particularly limited, and can be formed into, for example, a semicircle or a triangle by changing the shape of the groove 6. Further, by providing the groove 6 in both the substrate 2 and the top plate 3, it can be formed into a circle, an ellipse, a pentagon, other polygons, or the like.

  The microchannel 4 is not limited to the one formed by joining the substrate 2 provided with the groove 6 provided with the photocatalyst layer 5 and the top plate 3 as in the present embodiment, but has a circular cross section or a multi-section. It can be formed by providing a photocatalyst on the inner wall of a square capillary.

  The channel diameter of the microchannel 4 can be 10 to 2000 μm, preferably 50 to 1000 μm, and more preferably 100 to 500 μm. Here, the “channel diameter of the microchannel 4” is a length that defines the size of the reaction channel. For example, the cross section of the microchannel 4 has a short side length in a quadrangle, a diameter in a circle, and an elliptical shape. Means the short diameter. The length of the long side in the cross-sectional quadrangle and the length of the long diameter in the cross-sectional ellipse are particularly limited as long as the entire microchannel 4 can be irradiated with light and the mechanical strength of the reactor can be maintained. For example, the ratio of the length of the long side / the length of the short side and the ratio of the long diameter / short diameter may be about 1 to 20.

  Further, as shown in FIG. 6, the photocatalyst layer 5 is not provided on the top plate 3 on the top surface of the microchannel 4, and the inner surface of the groove 6 of the substrate 2, that is, on the side wall surface and the bottom surface of the microchannel 4. By providing the photocatalyst only in this manner, the photocatalyst can be efficiently irradiated with light from the upper surface of the top 3. Thus, when irradiating light with respect to the photocatalyst provided in the groove | channel 6 inner surface of the board | substrate 2 from the upper surface side of the top plate 3, it is set as the structure by which only this top plate 3 is formed with the transparent material. It is also possible.

  A first supply port 11 for supplying the raw material to the micro flow path 4 is provided at one end of the groove 6 provided in the substrate 2. Further, the top plate 3 is provided with a second supply port 12 at a position substantially opposite to the first supply port 11 when bonded to the substrate 2. Further, the top plate 3 is provided with a takeout port 13 through which the reaction solution that has passed through the microchannel 4 is taken out.

  One of the first supply port 11 and the second supply port 12 is used as a supply port for carbon dioxide, which is a gaseous material, and the other is used as a supply port for a liquid material capable of generating an organic compound. In the present embodiment, the first supply port 11 is described as a carbon dioxide supply port, and the second supply port 12 is described as a liquid material supply port capable of generating an organic compound.

  Tube connectors 18 are provided at the first supply port 11 and the second supply port 12. The first supply port 11 is connected to a gas raw material syringe pump 16 which is a gas raw material feed means via a microtube 14, and the second supply port 12 is a liquid raw material feed means via a microtube 15. The liquid source syringe pump 17 is connected. As the gas raw material feeding means and the liquid raw material feeding means, in addition to the syringe pump, a device capable of adjusting the gas or liquid supply speed can be used.

  The gas raw material syringe pump 16 and the liquid raw material syringe pump 17 adjust the supply speed of the liquid raw material capable of generating carbon dioxide, which is the gaseous raw material, and the organic compound, and the liquid raw material follows the inner surface of the microchannel 4. The pipe flow in a state where carbon dioxide flows through the central portion can be formed. The reaction solution that has passed through the microchannel 4 is taken out from the takeout port 13.

In order to irradiate the photocatalyst layer 5 with light in order to induce a photoreaction, it is desirable to use a light irradiation device 8 using an ultraviolet light emitting diode 19 as a light source. By using a light emitting diode as a light source of the light irradiation device 8, space saving and low photon cost of the photocatalytic micro device 1 can be realized. In the light irradiation device 8, light is provided on the top surface of the top plate 3, and the ultraviolet light emitting diodes 19 are arranged in series along the microchannel 4.
When a visible light responsive photocatalyst is used for the photocatalyst layer 5, sunlight can be used as an excitation light source for the photocatalyst, so that no light irradiation device is required.

  FIG. 7 shows another example of the microchannel 4 provided with the photocatalyst layer 5 described with reference to FIG. That is, the photocatalyst layer 5 can be formed on a portion of the top plate 3 that forms the upper surface of the microchannel 4, and the photocatalyst can be provided on the entire surface of the microchannel 4. In this case, the photocatalyst layer 5 is desirably formed thin enough to transmit the light irradiated by the light irradiation device 8. As described above, when the photocatalyst is provided on the entire surface of the microchannel 4, a light irradiation device (not shown) is further provided on the lower surface side of the substrate 2, and light is transmitted from the upper surface and the lower surface of the microchannel 4. It is preferable to be configured to be irradiated. Further, when the photocatalyst is formed on the entire surface of the microchannel 4, the photocatalyst layer 5 is formed in a slit shape so that the light irradiated by the light irradiation device 8 can be easily transmitted into the microchannel 4. You can also.

(Example 2)
Next, the carbon dioxide immobilization reaction performed by the carbon dioxide immobilization apparatus 1 described in the first embodiment will be described in the case of using water (H ₂ O) as a liquid raw material that can react with carbon dioxide to generate an organic compound. To do.

  Carbon dioxide, which is a gaseous raw material, is introduced from the first supply port 11 of the carbon dioxide fixing device 1. Water is introduced from the second supply port 12 as a liquid raw material that can react with carbon dioxide to produce an organic compound. The carbon dioxide and water supply rates are adjusted by the gas raw material syringe pump 16 and the liquid raw material syringe pump 17, respectively, and the cylindrical liquid film flow in which water flows along the inner surface of the microchannel 4 and the carbon dioxide in the center. It is set to form a pipe flow consisting of a central gas flow in a state of flowing through the section.

  Thus, by forming a pipe flow with carbon dioxide, which is a gaseous raw material, with respect to water, which is a liquid raw material, water in which carbon dioxide is dissolved in a saturated state is forcibly localized near the surface of the photocatalyst layer 5. Thus, the photocatalytic reaction can be performed by passing the microchannel 4 in a laminar flow state.

  Furthermore, since carbon dioxide comes into contact with water in the vicinity of the photocatalyst layer 5, even if carbon dioxide dissolved in water is consumed as the photocatalytic reaction proceeds, carbon dioxide is always supplied from the central gas stream. . Therefore, the concentration of carbon dioxide dissolved in the cylindrical liquid film flow of water can always be kept constant in a saturated state over the entire length of the microchannel 4, and the photocatalytic reaction can proceed with high efficiency. Can do.

[Specific example of fixing carbon dioxide as methanol by pipe flow]
In the carbon dioxide immobilization apparatus 1 used, the depth of the microchannel 4 is 40 μm, the width is 100 μm, the length is 200 mm, the main wavelength of the ultraviolet light emitting diode 19 is 365 nm, and the output is 450 mW. Pure water was used as the liquid raw material. Further, as a photocatalyst, and titanium dioxide (TiO _2), it was performed on two types of titanium dioxide of carrying platinum as a cocatalyst _(TiO 2 / Pt).

  The flow rate of pure water is set to 10 μL / min (microliter / minute), the flow rate of carbon dioxide is adjusted to form a pipe flow as shown in FIG. Light irradiation by the diode 19 was performed. The flow rate of carbon dioxide (μL / min) is set to 0 (flow that does not form a pipe flow), 50, 100, 150, and 200, and each reaction product taken out from the take-out port 13 is subjected to gas chromatography and generated. The amount of methanol produced (concentration mM) was measured.

  FIG. 8 shows the measurement results. The horizontal axis represents the flow rate of carbon dioxide (μL / min), and the vertical axis represents the yield of methanol (concentration mM). By the way, if the pipe flow is formed with the liquid flow rate (μL / min) kept constant, the liquid film thickness decreases as the gas flow rate increases. Therefore, in the pipe flow, there is a relationship that the residence time of the liquid in the micro-channel gradually becomes shorter as the gas flow rate becomes faster.

FIG. 9 shows the production amount per unit time so as not to be affected by the difference in length of the residence time. That is, in FIG. 9, the horizontal axis represents the flow rate of carbon dioxide (μl / min), and the vertical axis represents the methanol yield per unit time (mM / sec).
From FIG. 9, it can be understood that, by forming a pipe flow and advancing the photocatalytic reaction, the yield of methanol per unit time is increased and the reaction is efficiently performed. That is, the amount of methanol produced by the photocatalytic reaction could be effectively increased.

  The residence time of the reaction liquid in the micro flow path can be calculated using a model for exchanging momentum between gas and liquid in the pipe flow by LEVY. According to this calculation, when the flow rate of carbon dioxide is 0, the residence time of the reaction solution in the microchannel is 26.3 seconds, and when the flow rate of carbon dioxide is 50 μL / min, 9.3 seconds and 100 μL. It is 5.3 seconds at / min, 4.1 seconds at 150 μL / min, and 3.6 seconds at 200 μL / min.

[Relationship between pipe flow and cocatalyst effect]
Next, the photocatalytic reaction of methanol generation proceeds by forming a pipe flow, so that the effect of the cocatalyst is diminished, that is, the pipe flow may replace the improvement of the catalytic activity by the cocatalyst. explain.

FIG. 10 excludes the portion where the flow rate of carbon dioxide that does not form a pipe flow in FIG. 9 is 0, and FIG. 9 shows the platinum support when the platinum promoter is used on the vertical axis (TiO ₂ / Pt). It is rewritten in place of the yield ratio with respect to the case where no catalyst is used (TiO ₂ ). That is, the vertical axis shows the effect of the promoter. FIG. 10 shows that the effect of the promoter is about 1.2 times at the maximum.

  On the other hand, Table 1 shows that no pure gas saturated with carbon dioxide is supplied to the micro flow path without injecting gas, that is, without forming a pipe flow, and the photocatalytic reaction proceeds to collect methanol for each catalyst. The result of measuring the rate (concentration mM) is shown. For reference, the measurement results of the batch reactor were also shown.

In Table 1, when the platinum promoter is used (TiO ₂ / Pt), the yield is 2.4 mM, while when the platinum promoter is not used (TiO ₂ ), the yield is 0.09 mM. The effect of the cocatalyst is more than 20 times.

  From the above, the effect of the cocatalyst when the pipe flow is formed is “about 1.2 times”, which is much smaller than the effect of the cocatalyst when the pipe flow is not formed “more than 20 times”. I can say that. That is, it can be said that the pipe flow can replace the improvement of the catalytic activity by the cocatalyst.

8 and 9, when the flow rate of carbon dioxide is 50 μL / min, the pipe flow is not in a complete form, and is in a slag flow state in which gas and liquid alternately flow. In this slag flow part, the yield when using the platinum promoter (TiO ₂ / Pt) is lower than the yield when not using the platinum promoter (TiO ₂ ). The result is a negative effect. The reason for this is not clear, but slag flow is thought to have brought about such a result.

  Here, since the photocatalytic reaction is a reaction accompanied by a reverse reaction, if formic acid, formaldehyde, methanol, and methane generated by reaction with carbon dioxide are present in the reaction system (in a cylindrical liquid film flow of water), reduction occurs. An oxidation reaction, which is the reverse reaction of the reaction, causes a reaction in which they return to carbon dioxide. However, when the pipe flow is formed, among the formic acid, formaldehyde, methanol, and methane produced by reacting with carbon dioxide in the water, methane has a high vapor pressure and low solubility in water as a liquid raw material. Tends to move into the central gas stream of the pipe flow.

  In this way, the produced methane escapes from the reaction system (in the cylindrical liquid film flow of water) into the central gas flow, so that the reverse reaction by the photocatalyst of the produced methane is prevented, and the methane having a high vapor pressure. Can be obtained efficiently.

  In addition, since the produced methanol has high solubility in water, it tends to remain in the cylindrical liquid film flow of water and is taken out from the water as a product, but also moves into the central gas flow because of its high vapor pressure, and the aforementioned As in the case of methane, the reverse reaction is prevented for the methanol component that has moved into the central gas stream, and the methanol can be produced with high efficiency.

  The present invention is effective as a carbon dioxide immobilization apparatus and a carbon dioxide immobilization method using a photocatalyst.

It is a figure explaining reaction in the carbon dioxide immobilization device concerning the present invention. It is a figure explaining the reaction at the time of using the water source as a liquid raw material in the carbon dioxide fixing device which concerns on this invention. 1 is a perspective view showing a carbon dioxide immobilization device according to Example 1. FIG. It is II sectional drawing of FIG. It is an enlarged view of the A section of the II-II section of Drawing 4, and is a figure showing the pipe flow state in a micro channel. It is III-III sectional drawing of FIG. It is another example of the microchannel provided with the layer of the photocatalyst. It is a figure which shows the measurement result of the yield (concentration mM) of methanol with respect to the flow rate (microliter / min) of a carbon dioxide. FIG. 8 is a diagram obtained by rewriting FIG. 8 by setting the vertical axis as the generation amount per unit time so as not to be affected by the difference in length of the residence time in the liquid microchannel. In FIG. 9, when the flow rate of carbon dioxide that does not form a pipe flow is excluded, the vertical axis represents the case where the platinum promoter is used (TiO ₂ / Pt) and the platinum promoter is not used (TiO ₂ It is a figure rewritten by changing the ratio of the yield to).

Explanation of symbols

1 carbon dioxide fixing device, 2 substrate, 3 top plate,
4 microchannels, 5 photocatalyst layers, 6 grooves,
8 light irradiation device, 10 microreactor,
11 First supply port (carbon dioxide supply port),
12 Second supply port (liquid material supply port),
13 outlet, 14, 15 microtube,
16 Syringe pump for gas raw material (gas raw material feeding means),
17 Liquid raw material syringe pump (liquid raw material feeding means),
18 Tube connector, 19 UV light emitting diode

Claims (6)

A microreactor having a microchannel through which a gas raw material and a liquid raw material are circulated as a reaction raw material;
Gaseous raw material feeding means for feeding the gaseous raw material into the microchannel;
Liquid raw material feeding means for feeding the liquid raw material into the microchannel;
A photocatalyst layer provided on the inner surface of the microchannel,
The gaseous raw material is carbon dioxide, and the liquid raw material is a raw material that can react with carbon dioxide to produce an organic compound,
The gaseous raw material feeding means and the liquid raw material feeding means are configured to be capable of forming a pipe flow in which the liquid raw material flows along the inner surface of the microchannel and carbon dioxide flows through the central portion. Carbon dioxide immobilization device.   2. The carbon dioxide immobilization apparatus according to claim 1, wherein the photocatalyst is titanium dioxide.   3. The carbon dioxide immobilization apparatus according to claim 2, wherein any one of ruthenium, rhodium, palladium, platinum, copper, silver, and gold is supported on the titanium dioxide as a promoter. A carbon dioxide immobilization device that is characterized. Carbon dioxide as a gas raw material is fed into the microchannel of the microreactor having a photocatalyst layer on the inner surface of the microchannel, and a raw material that can react with the carbon dioxide as a liquid raw material to generate an organic compound,
The liquid raw material flows along the inner surface of the microchannel in the microchannel, and the organic compound is generated from the carbon dioxide by forming a pipe flow in a state where the carbon dioxide flows through the central portion to advance the photocatalytic reaction. And immobilizing carbon dioxide to fix the carbon dioxide.   The method for immobilizing carbon dioxide according to claim 4, wherein the liquid raw material is water, and at least one compound of formic acid, formaldehyde, and methane is produced as a carbon dioxide reduction product. Carbon dioxide immobilization method. 5. The carbon dioxide immobilization method according to claim 4, wherein the liquid raw material is water, and methanol is generated as a carbon dioxide reduction product.

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